A new study has shown selective nanotherapy could be a safe and effective treatment to prevent serious viral infection with SARS-CoV-2.
SARS-CoV-2 enters host cells via a complex process that requires specific host proteases, such as TMPRSS2 and Cathepsin L (Ctsl). Studies that inhibited Ctsl have not proven to be effective at preventing SARS-CoV-2 infection in vivo, since the virus can gain entry into cells using alternative proteases such as TMPRSS2.
There are also problems with this approach. Cathepsins such as Cathepsin L are vital for normal physiological processes, including the immune response. While the severity of SARS-CoV-2 infection could potentially be reduced, using gene therapy to knock out the Ctsl gene is far from ideal as the gene would be permanently removed, which could have unintended consequences and the use of cathepsin inhibitors does not provide the degree of specificity needed.
A team of researchers has developed a new method that involves a transient knockdown of Ctsl mRNA transcripts using CRISPR/CasRx – a CRISPR/Cas13d-based nanoparticle therapy. This method is highly specific and can knockdown Ctsl mRNA without affecting the expression of other cathepsins, allowing the processes that they regulate to continue. While viruses can mutate to render treatments ineffective, most viruses do not mutate at a high rate in the Ctsl target site, so this approach could be effective at both preventing and treating viral infections.
The researchers used this new approach in an in vivo study on mice that expressed human ACE2 receptors. The mice were given a lethal dose of SARS-CoV-2 after being treated with LNP-CasRx-pre-gCtsl and were protected against the cytokine storm that leads to severe lung pathology.
After treatment, there was a reduced viral load and a corresponding reduction in levels of cytokines and chemokines, and in vitro studies showed treatment suppressed entry of SARS-CoV-2 into cells irrespective of whether the cells expressed the protease TMPRSS2, indicating Ctsl is required for viral entry via several different pathways.
“Our results demonstrate the efficacy and safety of a lung-selective, Ctsl-targeted nanotherapy against infection by SARS-CoV-2 and likely other emerging coronaviruses, forming a basis for investigation of this approach in clinical trials,” explained the researchers in the paper.
The LNP-CasRx-pre-gCtsl was also shown to prevent the entry of pseudoviruses into cells. Pseudoviruses are viruses that have been engineered so they cannot replicate, which means they can be used as a model for scientists to study safely, without having to comply with many of the biosafety guidelines that are required for highly infectious diseases, including SARS-CoV-2, tuberculosis, and Ebola. That means the door is opened for much more extensive research into the potential use of this method of treatment or prophylaxis to prevent serious illness caused by other coronaviruses.
You can read more about the research in the paper – Lung-selective Cas13d-based nanotherapy inhibits lethal SARS-CoV-2 infection by targeting host protease Ctsl – a preprint of which is available on bioRxiV ahead of the peer-review process. DOI: 10.1101/2021.10.03.462915